We used DTI to explore anatomical accounts for individual differences in the behavioral effects of value-directed remembering. We examined connectivity within the mesolimbic system by using probabilistic tractography algorithms to compute anatomical connectivity between each subject’s nucleus accumbens(NAcc) and ventral tegmental area(VTA). We also extracted mean fractional anisotropy (FA) values from each subject’s uncinate fasciculus(UF). Subject’s engaged in a value-directed remembering task where each word was paired with either high or low values. Subject’s mean FA along their UF was strongly correlated with the mean number of high value words they reported during recall (r=.746, p=.0001), but not with number of low value words recalled(r=.219, p=.81). The difference between these two correlations was statistically significant (Z=2.46, p=.006). The number of streamlines (i.e, the Anatomical Connectivity Index) from left NAcc to left VTA correlated with Selectivity Index(i.e how preferentially selective they were in selectively recalling high value words more so than low value words) (r=.482, p=.018).

When given a long list of items to remember, people will often prioritize the memorization of the most important items. In an experimental setting, importance can be operationalized by reward values assigned to each item. Prior neuroimaging studies (e.g., Adcock et al., 2006) have found that high value cues engage the mesolimbic dopamingeric reward circuitry of the brain, including the nucleus accumbens (NAcc) and the ventral tegmental area (VTA), which it turn leads to an up-regulation of medial temporal lobe encoding processes and better memory for the high value items. Value cues may also trigger the use of elaborative semantic encoding strategies, which depend on interactions between frontal and temporal lobe structures. In the present study, we used diffusion tensor imaging (DTI) to examine whether individual differences in anatomical connectivity within these circuits are predictive of value-induced modulation of memory. DTI data were collected from 19 healthy adult subjects, who also underwent fMRI scanning as they performed a value-directed memory task. In this task, subjects encoded lists of words with arbitrarily assigned point values and then completed a free recall test after each list. Our fMRI results revealed that subjects whose recall performance exhibited the greatest sensitivity to item value preferentially recruited left ventrolateral prefrontal cortex (VLPFC) duringthe encoding of high value items relative to low value items. While this effect may partially be driven by individual differences in the cognitive strategies that foster deep semantic encoding, we predicted that the robustness of the white matter pathways connecting the VLPFC with the temporal lobe might also be a determinant of recall performance for high value items. To explore this possibility, we measured the mean fractional anisotropy (FA) of each subject’s left uncinate fasciculus, a pathway thought to play a critical role in semantic processing (Harvey et al., 2013). This measure showed a significant positive correlation with the mean number of high value items that a subject recalled, but did not correlate with the mean number of low value items recalled. Given prior findings on reward-induced modulation of memory, we also examined the white matter connections between reward-related regions such as the NAcc and VTA using probabilistic tractography. As predicted, the number of fibers projecting from left NAcc to VTA correlated with individual differences in high value but not low value memory. Together, these findings provide novel insights into the neuroanatomical pathways that support verbal memory encoding and its value-incentivized modulation.